Effect of ultrasound thawing, vacuum thawing, and microwave thawing on gelling properties of protein from porcine longissimus dorsi.

Effect of new thawing methods (ultrasound thawing (UT), vacuum thawing, (VT), microwave thawing (MT)) on gelling properties of myofibrillar protein (MP) from porcine longissimus dorsi was investigated, compared with traditional thawing methods (water immersion thawing, (WT)) and fresh meat (FM). The results showed that a decrease in MP gelling properties of all thawing samples was observed. The increase in roughness of MP gel from all thawing samples explained that the flatter, smoother, and denser surface morphology of that from FM samples was destroyed based on the observation by atomic force microscopy. There was significant difference (P < 0.05) in all gel indicators (particle size, turbidity, whiteness, water-holding capacity (WHC), moisture distribution, rheological characteristics, surface morphology) of MP from MT samples and there was insignificant difference (P > 0.05) in turbidity, whiteness, WHC of MP from VT samples compared with that from FM samples. There was insignificant difference (P > 0.05) in gel properties between UT and VT. The effect of UT and VT (new thawing methods) on MP gelling properties was significantly lower (P < 0.05) than that of WT (traditional thawing methods), and the effect of that from MT was obviously compared with other thawing methods.

Effects of different thawing methods on physicochemical properties and structure of largemouth bass (Micropterus salmoides).

To evaluate the physicochemical properties and structure of thawed fillets, following six treatments were used: conventional thawing, microwave thawing, microwave or ultrasound combined with vacuum thawing, magnetic nanoparticles combined with microwave or far-infrared thawing. The thawing loss, cooking loss, pH, color, texture change, water-holding capacity, and water migration of fish fillets were determined. The total volatile base nitrogen and thiobarbituric acid were used to determine the degree of protein degradation and lipid oxidation. Microscope observations and scanning electron microscope (SEM) were used to observe fiber microstructure. Results indicated that both microwave combined with vacuum thawing and far-infrared combined with magnetic nanoparticles thawing had desirable physicochemical properties as compared to other thawing methods. The lower total volatile base nitrogen and thiobarbituric acid values had less effect on protein degradation and lipid oxidation of thawing process. Besides, both microwaves combined with vacuum thawing and far-infrared combined with magnetic nanoparticles thawing samples had no significant difference in immobilized and bond water compared with fresh sample. SEM and microscopic observation showed that the myofibril bundles were arranged regularly and smoothly in microwave combined with vacuum thawing and far-infrared combined with magnetic nanoparticles thawing samples compared with other thawed methods. Thus, the microwave combined with vacuum thawing and far-infrared combined with magnetic nanoparticles thawing as potential thawing methods could be used to maintain the quality of thawed fish fillets. PRACTICAL APPLICATION: Largemouth bass (Micropterus salmoides) is a good source of animal protein. The fish needs to be frozen for circulation because of geographical and seasonal factors, so thawing methods can directly affect the quality of thawed fish. The results showed that the microwave combined with vacuum and the magnetic nanoparticles combined with far-infrared thawing could better maintain the quality of thawed fish.

Effects of different thawing methods on conformation and oxidation of myofibrillar protein from largemouth bass (Micropterus salmoides).

This study examined the effects on conformation and oxidation of myofibrillar protein in largemouth bass by different thawing methods. The conventional thawing, microwave thawing, microwave (MVT) or ultrasound combined with vacuum thawing, microwave or far-infrared thawing (FMT) combined with magnetic nanoparticles were used in this experiment. The physicochemical changes were analyzed by differential scanning calorimetry and dynamic rheology. The protein structure changes were measured by Raman, intrinsic fluorescence, and second-derivative ultraviolet spectrometry. The degree of protein aggregation was evaluated by surface hydrophobicity, particle size, and zeta-potential measurements. Total sulfhydryl content, protein carbonyl content, Ca2+ -ATPase activity, and SDS-PAGE were used to analyze the degree of protein oxidation. Results showed that MVT and FMT samples had better thermal stability, more stable protein conformation, and a lower degree of protein oxidation. Thus, these two methods would be beneficial to sustain the quality of thawed fillets. PRACTICAL APPLICATIONS: In the market circulation, largemouth bass (Micropterus salmoides) need to be frozen. The thawing methods can directly affect the quality of frozen fish, thus causing the changes in the conformation of the myofibrillar protein in fish, and also affecting the degree of protein oxidation. The results showed that the microwave combined with vacuum and the magnetic nanoparticles combined with far-infrared thawing had less effect on myofibrillar protein of fish and were a better thawing method.

Ultrasound or microwave vacuum thawing of red seabream (Pagrus major) fillets.

Ultrasound assisted vacuum thawing (UVT) or microwave vacuum thawing (MVT) with red seabream fillets were compared to fresh, chill storage thawing, vacuum thawing, microwave thawing and ultrasound thawing. The thermal stability and gelation properties were studied with DSC and dynamic rheology, respectively. Raman spectra before and after H/D isotope exchange and intrinsic fluorescence were used to measure protein secondary and tertiary structure. Low-field NMR was done to measure water migration. The two thawing techniques both retained actin thermal stability and generally retained more stable tertiary structures than the other thawing methods. MVT showed a desirable viscoelasticity of muscle proteins and UVT had a relatively stable secondary structure. There were no significant changes in free water. Thus, UVT and MVT could be used to improve the physicochemical properties of proteins during thawing of fillets.